arthas/tutorials/katacoda/command-jad-en/jad.md

Decompile the specified classes.

jad helps to decompile the byte code running in JVM to the source code to assist you to understand the logic behind better.

• The decompiled code is syntax highlighted for better readability in Arthas console.
• It is possible that there's grammar error in the decompiled code, but it should not affect your interpretation.

Options

Name	Specification
class-pattern	pattern for the class name
[c:]	hashcode of the class loader that loads the class
[E]	turn on regex match while the default is wildcard match

Usage

Decompile java.lang.String

jad java.lang.String{{execute T2}}

$ jad java.lang.String

ClassLoader:

Location:


/*
* Decompiled with CFR 0_132.
*/
package java.lang;

import java.io.ObjectStreamField;
...
public final class String
implements Serializable,
Comparable<String>,
CharSequence {
    private final char[] value;
    private int hash;
    private static final long serialVersionUID = -6849794470754667710L;
    private static final ObjectStreamField[] serialPersistentFields = new ObjectStreamField[0];
    public static final Comparator<String> CASE_INSENSITIVE_ORDER = new CaseInsensitiveComparator();

    public String(byte[] arrby, int n, int n2) {
        String.checkBounds(arrby, n, n2);
        this.value = StringCoding.decode(arrby, n, n2);
    }
...

Print source only

By default, the decompile result will have the ClassLoader information. With the --source-only option, you can print only the source code. Conveniently used with the mc/redefine commands.

jad --source-only java.lang.String{{execute T2}}

$ jad --source-only java.lang.String
...
        @Override
        public int compare(String string, String string2) {
            int n = string.length();
            int n2 = string2.length();
            int n3 = Math.min(n, n2);
            for (int i = 0; i < n3; ++i) {
                char c;
                char c2 = string.charAt(i);
                if (c2 == (c = string2.charAt(i)) || (c2 = Character.toUpperCase(c2)) == (c = Character.toUpperCase(c)) || (c2 = Character.toLowerCase(c2)) == (c = Character.toLowerCase(c))) continue;
                return c2 - c;
            }
            return n - n2;
        }

        private Object readResolve() {
            return String.CASE_INSENSITIVE_ORDER;
        }
    }
}

Decompile the specified method

jad java.lang.String toString{{execute T2}}

$ jad java.lang.String toString

ClassLoader:

Location:


@Override
public String toString() {
    return this;
}

Affect(row-cnt:2) cost in 407 ms.

Decompile with specified classLoader

If the target class is loaded by multiple classloaders, jad outputs the hashcode of the corresponding classloaders, then you can re-run jad and specify -c <hashcode> to decompile the target class from the specified classloader.

Examples:

$ jad org.apache.log4j.Logger

Found more than one class for: org.apache.log4j.Logger, Please use jad -c hashcode org.apache.log4j.Logger
HASHCODE  CLASSLOADER
69dcaba4  +-monitor's ModuleClassLoader
6e51ad67  +-java.net.URLClassLoader@6e51ad67
            +-sun.misc.Launcher$AppClassLoader@6951a712
            +-sun.misc.Launcher$ExtClassLoader@6fafc4c2
2bdd9114  +-pandora-qos-service's ModuleClassLoader
4c0df5f8  +-pandora-framework's ModuleClassLoader

Affect(row-cnt:0) cost in 38 ms.

$ jad org.apache.log4j.Logger -c 69dcaba4

ClassLoader:
+-monitor's ModuleClassLoader

Location:
/Users/admin/app/log4j-1.2.14.jar

package org.apache.log4j;

import org.apache.log4j.spi.*;

public class Logger extends Category
{
    private static final String FQCN;

    protected Logger(String name)
    {
        super(name);
    }

...

Affect(row-cnt:1) cost in 190 ms.